1. Field of the Invention
The present invention relates to a method of decreasing endpoint detection noise in a chemical-mechanical polishing process. More particularly, the present invention relates to a method of decreasing endpoint detection noise in a chemical-mechanical polishing process by using anti-reflective layer.
2. Description of the Related Art
Chemical-mechanical polishing is the only technique capable of providing the global planarization in VLSI process, and even in ULSI process.
A reflectometer or a spectometer is used as an end point detector in a chemical-mechanical polishing process. However, it is difficult to detect the end point when the incident light is reflected by the different material layers because the reflected lights of the different material layers interfere with each other.
FIG. 1 is a schematic, cross-sectional diagram used to depict the effect of the reflected light on end point detector in a chemical-mechanical polishing process.
A patterned material layer 12 is formed on a provided substrate 10. The material layer 12 having an opening 16 is formed by photolithographic etching. The opening 16 exposes the substrate 10. A thick material layer 14 is formed on the material layer 12 and fills the opening 16. The material of the material layer 12 and the material layer 14 are different. Chemical-mechanical polishing is performed to planarize the material layer 14. When an incident light I.sub.0 from the end point detector such as a reflectometer or a spectometer irradiates the different material layers, different reflected lights are produced.
As shown in FIG. 1, the reflected light I.sub.1 is produced when the incident light I.sub.0 irradiates the material layer 12. The reflected light I.sub.2 is produced while the incident light I.sub.0 irradiates the substrate 10 exposed by the opening 16. During a chemical-mechanical polishing process, the end point is verified by using the reflected lights. The choice of the reflected lights is based on the material of the material layer 14. If the end point is verified by the change of the intensity of the reflected light I.sub.1, the reflected light I.sub.2 interferes with the reflected light I.sub.1. Similarly, if the end point is verified by the change in the intensity of the reflected light I.sub.2, the reflected light I.sub.1 interferes with the reflected light I.sub.2.